The present invention generally relates to medical devices, especially to tubing that exhibits improved properties which are especially suitable for various medical devices such as catheters and the like. More particularly, the invention relates to medical device tubing components which are extruded from a blend of at least two polymers, one of which is a polyetheramide. As used herein, the polyetheramide is one which has no ester linkages or has only incidental ester linkages, hereinafter referred to as having substantially no ester linkages. Advantageously, the polyetheramide component is blended with another polyamide-type of material in order to provide physical properties which are especially suitable for extrusion into catheter wall components and/or tip components. The polyetheramide-containing tubing is particularly suitable for medical device uses because the extruded polymer material exhibits excellent burst strength properties and good flexibility while at the same time retarding blooming that is experienced by other polyamide-types of tubing when they are stored for extended time periods.
Many medical devices incorporate tubing of various types and lengths. Often this tubing is intended for insertion into a living body, typically into and through body passageways such as those of the cardiovascular system, of the urethral tract, and the like. The most common type of this general grouping of medical devices are known as catheters, and they can incorporate tubing in body, balloon and tip members thereof. Exemplary catheters include those designed for angioplasty, valvuloplasty, urological uses, and the like. Typically, these devices are inserted into a body passageway such as the lumen of a blood vessel, a heart passageway, a urological passageway and the like, often with fluoroscopic guidance.
When medical devices are intended for use within the human body, certain parameters need to be satisfied. Usually the tubing must exhibit adequate flexibility so that, for example in the case of catheters, the tubing can easily wind its way through passageways which include bends and the like whereby the tubing can traverse a pathway through, for example, branching blood vessels. Furthermore, in many instances a catheter is manipulated from a proximal location outside of the body in order to position the distal portion of it in the vicinity of the administration or treatment location. In such systems or assemblies, it is important that the catheter exhibit adequate torque control so that it can be manipulated through narrow and branching passageways by radial movements and the like while having enough longitudinal or column resistance to negotiate through these passageways.
Another strength characteristic which is important for medical devices such as angiographic catheters, whether braided or unbraided, other balloon dilatation catheters and the like is burst strength. In some of these applications, fluids such as radiopaque dye containing fluids are injected under relatively high pressures through the medical device in a short time, for example, to provide a clear picture which is taken for a diagnostic purpose by an attending physician. This relatively high pressure injection achieves a high concentration of fluid in a short period of time so that images obtained during angiography and the like are as sharp as possible. Burst strength is also an important consideration for devices such as balloon catheters which include tubing components that are collapsed when inserted into the body cavity or the like and which are filled with a fluid so as to open up in a generally radial manner in order to open up a restricted passageway, for example, within the body. With these types of devices, an advantageous combination of high burst strength and flexibility are also important.
Quite a wide variety of materials have been used and proposed for manufacturing medical device tubing. Often, these materials are varied so that leading portions or tips of catheters and the like are somewhat more flexible and less traumatic than other portions of a catheter tubing which must be more responsive to manipulations that direct the device through the body. Exemplary in this regard is Ruiz U.S. Pat. No. 4,385,635, incorporated hereinto by reference. Certain approaches have been taken along these lines which concentrate on the use of polyamide types of materials for the manufacture of soft-tipped catheters, balloon catheters, catheter introducers, guiding catheters, vascular prostheses and the like. Included are Wijayarathna et al. U.S. Pat. No. 4,563,181, Lovgren et al. U.S. Pat. No. 4,886,506, Jang et al. U.S. Pat. No. 4,898,591, Jackson U.S. Pat. No. 4,917,667 and Hibbs et al. U.S. Pat. No. 4,950,257, each being incorporated by reference hereinto. These patents are representative of art relating to the use of polyether block amides, sometimes referred to by the designation PEBA. These are polyether-polyamide copolymers.
References such as the Wijayarathna et al. patent, the Jang patent and the Hibbs et al. patent explicitly teach that these polyether block amides are ester-linked polyether-polyamide copolymers which are described as being soft, rubbery polymeric materials. References such as these further indicate that these ester-linked polyether block amides are compatible with and fusible to polyamides or nylons by heat and pressure, while further indicating that the ester-linked polyether block amides can be blended with nylon polyamides such as Nylon 11, with different blends being suitable for different needs. For example, it is possible to blend these materials to provide a more flexible or softer extruded polymer that is more suitable for a tip portion of a catheter, while a different blend is less flexible and provides an extruded tubing that is more suitable for a catheter body requiring good torque control.
It has been found, however, that many of these polymers do not provide adequate burst strength properties and especially do not afford an extremely high burst strength to flexibility ratio which can be important for especially difficult medical device tubing applications. Another shortcoming of polymers or polymer blends such as the PEBA polyether block amide or ester-linked polyetherpolyamide copolymers is the development of undesirable blooming which develops in much of this tubing after it has been stored for lengths of time that can be experienced during the normal commercial channels through which medical devices pass. Accordingly, at times when a medical professional removes a catheter or the like from its sterilized packaging, a quite noticeable quantity of blooming can be evident on the surface of the catheter, which can significantly reduce the confidence level that the medical professional has in the catheter. This has the potential of being detrimental to the supplier of the catheter and may result in loss of current and/or future sales.
It is currently believed that this blooming phenomenon is a manifestation of migration of monomers to the surface of the polymeric tubing. A fine white powder forms on the surface of the tubing as it ages at room temperature or after it has been subjected to heat treatment. This surface powder formation has the potential of adding to the foreign matter which enters the bloodstream or the like when the medical tubing contacts or otherwise communicates with the bloodstream or other portion of the body. Whether or not this represents a possible medical detriment, it nevertheless creates a perception of a product that is less than perfect. This is, of course, something to be avoided by suppliers of medical devices. For at least that reason alone, blooming is a phenomenon that is undesirable, and its avoidance can substantially increase the usefulness and value of the medical device.
Blooming can be detrimental for another reason. It is often desirable to provide a catheter or the like with a coating that is designed to impart lubricity or enhanced biocompatibility to the catheter, or to provide a means for administering a drug or the like. Blooming can interfere with these types of coatings, interfering with their adherence to the entirety of the catheter.
The present invention provides medical device components, particularly tubing for catheters and the like. The components are made from a polyetheramide material which can be extruded into a desired medical device component. The polyetheramide is a polyamide elastomer having substantially no ester linkages. It is preferred that the polyetheramide be blended with at least one other material falling within the general category of polyamide structures. Included in the grouping of other materials are polymers having polyamide structures per se as well as certain polyesteretheramides, especially those having a particularly high hardness such as Shore 70D or harder. When extruded, for example into tubing, the result is a material that has an extremely high burst strength to flexibility ratio and that retards blooming.
It is accordingly a general object of the present invention to provide improved medical device components, particularly tubing for catheters and the like.
Another object of the present invention is to provide an improved material and method for extruding medical device tubing.
Another object of this invention is to provide improved medical device tubing which incorporates polyetheramide materials that do not have any substantial ester linkages present within the polyetheramide.
Another object of the present invention is to provide improved polyetheramide or polyetheramide composition that exhibits an extremely high burst strength to flexibility ratio when extruded into medical device tubing.
Another object of this invention is to provide an improved polyamide-like or polyamide composition that retards blooming or the migration of monomers to the surface of tubing or the like which is extruded from the material.
These and other objects, features and advantages of the invention will be clearly understood through a consideration of the following detailed description.